As used herein, the terms “display management” or “display mapping” denote the processing (e.g., tone and gamut mapping) required to map an input video signal of a first dynamic range (e.g., 1000 nits) to a display of a second dynamic range (e.g., 500 nits). Examples of display management processes can be found in WIPO Publication Ser. No. WO2014/130343 (to be referred to as the '343 publication), “Display Management for High Dynamic Range Video,” and U.S. Provisional Application Ser. No. 62/105,139, (to be referred as the '139 Application), filed on Jan. 19, 2015, each of which is incorporated herein by reference in its entirety.
As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human visual system (HVS) to perceive a range of light intensity (e.g., luminance, luma) in an image, e.g., from darkest blacks (darks) to brightest whites (highlights). In this sense, DR relates to a ‘scene-referred’ light intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g., interchangeably.
A reference electro-optical transfer function (EOTF) for a given display characterizes the relationship between color values (e.g., luminance) of an input video signal to output screen color values (e.g., screen luminance) produced by the display. For example, ITU Rec. ITU-R BT. 1886, “Reference electro-optical transfer function for flat panel displays used in HDTV studio production,” (March/2011), which is incorporated herein by reference in its entity, defines the reference EOTF for flat panel displays based on measured characteristics of the Cathode Ray Tube (CRT). Given a video stream, any ancillary information is typically embedded in the bit stream as metadata. As used herein, the term “metadata” relates to any auxiliary information that is transmitted as part of the coded bitstream and assists a decoder to render a decoded image. Such metadata may include, but are not limited to, color space or gamut information, reference display parameters, and auxiliary signal parameters, as those described herein.
Most consumer HDTVs range from 300 to 500 nits peak luminance with new models reaching 1000 nits (cd/m2). As the availability of HDR content grows due to advances in both capture equipment (e.g., cameras) and displays (e.g., the PRM-4200 professional reference monitor from Dolby Laboratories), HDR content may be color graded and displayed on displays that support higher dynamic ranges (e.g., from 1,000 nits to 5,000 nits or more). Such displays may be defined using alternative EOTFs that support high luminance capability (e.g., 0 to 10,000 nits). An example of such an EOTF is defined in SMPTE ST 2084:2014 “High Dynamic Range EOTF of Mastering Reference Displays,” which is incorporated herein by reference in its entirety. In general, without limitation, the methods of the present disclosure were designed primarily for any dynamic range higher than SDR. However, the general methods could be applied to dynamic ranges lower than SDR, such as would occur with either high ambient or lower dynamic range displays, and still result in improvement over doing no compensation. As appreciated by the inventors here, improved techniques for the display of high-dynamic range images, especially as they relate to a changing viewing environment, are desired.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.